Download Genetics

Probability
& Genetics
.A. Learning goals


Explain the random process of
chromosome segregation and
distribution of alleles in gametes.
Predict possible combinations of alleles
in a zygote from the genetic makeup of
the parents.
B. Independent Assortment of Alleles


Gametes (sperm and egg) will
contain two alleles for each gene.
They are divided randomly during
meiosis.
Sperm + Egg
Yy
yy
Yy
Yy
yy
yy
*this random selection of alleles occurs for23 pairs
of chromosomes for thousands of genes !!!
Probability
C. Punnett Square Terminology






Homozygous: Individuals with identical alleles Ex.
RR, rr
Heterozygous: Individuals with different alleles ex.
Rr
Dominant: always expresses the trait
Rr, RR
Recessive: needs both recessive alleles to express
the trait
rr
Phenotype – physical characteristic
Ex. White fur, blue eyes, green skin
Genotype – genetic makeup
Ex. FF, Bb, or gg
How to use Punnett Squares




Choose a letter to represent the
alleles in the cross.
Write the genotypes of the parents.
Determine the possible gametes
(reproductive cells) that the parent
can produce.
Enter the possible gamete at the top
and side of the Punnett square.
D. Practice

Ex. 1
A plant that is homozygous recessive for short ,
_tt___, is crossed with a plant that is homozygous
for TT. How many offspring will be short?
T
t
t
Tt
Tt
T
Tt
Tt
Answer: O , all
will be tall and
heterozygous.
Ex. 2

The Rock has the heterozygous condition of rolling
tongue, Rr and his wife has the heterozygous
condition as well, Rr. They have four children. What
is the ratio
among the offspring
T of rolling tongue
T
R
r
R
RR
Rr
r
Rr
rr
Answer: 3:1 of
the offspring
have rolling
tongue!
Punnett Squares Monohybrid &
Dihybrid Crosses
Punnett Squares
Mendel’s Principles Summary




The inheritance of biological
characteristics are determined by genes.
For two or more forms of a gene,
dominance and recessive forms may
exist.
Most sexually reproductive organisms
have two sets of genes that separate
during gamete formation.
Alleles segregate independently.